xenocara/proto/xcb-proto/xcbgen/align.py

'''
This module contains helper classes for alignment arithmetic and checks
'''

from fractions import gcd

class Alignment(object):

    def __init__(self, align=4, offset=0):
        self.align = align
        # normalize the offset (just in case)
        self.offset = offset % align


    def __eq__(self, other):
        return self.align == other.align and self.offset == other.offset

    def __str__(self):
        return "(align=%d, offset=%d)" % (self.align, self.offset)

    @staticmethod
    def for_primitive_type(size):
        # compute the required start_alignment based on the size of the type
        if size % 8 == 0:
            # do 8-byte primitives require 8-byte alignment in X11?
            return Alignment(8,0)
        elif size % 4 == 0:
            return Alignment(4,0)
        elif size % 2 == 0:
            return Alignment(2,0)
        else:
            return Alignment(1,0)


    def align_after_fixed_size(self, size):
        new_offset = (self.offset + size) % self.align
        return Alignment(self.align, new_offset)


    def is_guaranteed_at(self, external_align):
        '''
        Assuming the given external_align, checks whether
        self is fulfilled for all cases.
        Returns True if yes, False otherwise.
        '''
        if self.align == 1 and self.offset == 0:
            # alignment 1 with offset 0 is always fulfilled
            return True

        if external_align is None:
            # there is no external align -> fail
            return False

        if external_align.align < self.align:
            # the external align guarantees less alignment -> not guaranteed
            return False

        if external_align.align % self.align != 0:
            # the external align cannot be divided by our align
            # -> not guaranteed
            # (this can only happen if there are alignments that are not
            # a power of 2, which is highly discouraged. But better be
            # safe and check for it)
            return False

        if external_align.offset % self.align != self.offset:
            # offsets do not match
            return False

        return True


    def combine_with(self, other):
        # returns the alignment that is guaranteed when
        # both, self or other, can happen
        new_align = gcd(self.align, other.align)
        new_offset_candidate1 = self.offset % new_align
        new_offset_candidate2 = other.offset % new_align
        if new_offset_candidate1 == new_offset_candidate2:
            new_offset = new_offset_candidate1
        else:
            offset_diff = abs(new_offset_candidate2 - new_offset_candidate1)
            new_align = gcd(new_align, offset_diff)
            new_offset_candidate1 = self.offset % new_align
            new_offset_candidate2 = other.offset % new_align
            assert new_offset_candidate1 == new_offset_candidate2
            new_offset = new_offset_candidate1
        # return the result
        return Alignment(new_align, new_offset)


class AlignmentLog(object):

    def __init__(self):
        self.ok_list = []
        self.fail_list = []
        self.verbosity = 1

    def __str__(self):
        result = ""

        # output the OK-list
        for (align_before, field_name, type_obj, callstack, align_after) in self.ok_list:
            stacksize = len(callstack)
            indent = '  ' * stacksize
            if self.ok_callstack_is_relevant(callstack):
                if field_name is None or field_name == "":
                    result += ("    %sok: %s:\n\t%sbefore: %s, after: %s\n"
                        % (indent, str(type_obj), indent, str(align_before), str(align_after)))
                else:
                    result += ("    %sok: field \"%s\" in %s:\n\t%sbefore: %s, after: %s\n"
                        % (indent, str(field_name), str(type_obj),
                           indent, str(align_before), str(align_after)))
                if self.verbosity >= 1:
                    result += self.callstack_to_str(indent, callstack)

        # output the fail-list
        for (align_before, field_name, type_obj, callstack, reason) in self.fail_list:
            stacksize = len(callstack)
            indent = '  ' * stacksize
            if field_name is None or field_name == "":
                result += ("    %sfail: align %s is incompatible with\n\t%s%s\n\t%sReason: %s\n"
                    % (indent, str(align_before), indent, str(type_obj), indent, reason))
            else:
                result += ("    %sfail: align %s is incompatible with\n\t%sfield \"%s\" in %s\n\t%sReason: %s\n"
                    % (indent, str(align_before), indent, str(field_name), str(type_obj), indent, reason))

            if self.verbosity >= 1:
                result += self.callstack_to_str(indent, callstack)


        return result


    def callstack_to_str(self, indent, callstack):
        result = "\t%scallstack: [\n" % indent
        for stack_elem in callstack:
            result += "\t  %s%s\n" % (indent, str(stack_elem))
        result += "\t%s]\n" % indent
        return result


    def ok_callstack_is_relevant(self, ok_callstack):
        # determine whether an ok callstack is relevant for logging
        if self.verbosity >= 2:
            return True

        # empty callstacks are always relevant
        if len(ok_callstack) == 0:
            return True

        # check whether the ok_callstack is a subset or equal to a fail_callstack
        for (align_before, field_name, type_obj, fail_callstack, reason) in self.fail_list:
            if len(ok_callstack) <= len(fail_callstack):
                zipped = zip(ok_callstack, fail_callstack[:len(ok_callstack)])
                is_subset = all([i == j for i, j in zipped])
                if is_subset:
                    return True

        return False


    def ok(self, align_before, field_name, type_obj, callstack, align_after):
        self.ok_list.append((align_before, field_name, type_obj, callstack, align_after))

    def fail(self, align_before, field_name, type_obj, callstack, reason):
        self.fail_list.append((align_before, field_name, type_obj, callstack, reason))

    def append(self, other):
        self.ok_list.extend(other.ok_list)
        self.fail_list.extend(other.fail_list)

    def ok_count(self):
        return len(self.ok_list)